Several types of safety caps for pressurized containers are known.
Generally, conventional safety caps comprise a closure member of the aperture of the container and a grip member which, depending on the pressure level inside the container, can rotate freely with respect of the closure member in order to prevent the removal of the cap when the pressure is too high.
By contrast, when the pressure inside the container is low, or at any rate below a dangerous value, the grip member is rigidly associated with the closure member by connecting means adapted to allow the user to remove the cap.
The connecting means between the grip member and the closure member of the safety cap can be activated by the motion of a slider inside the cap by the pressure generated inside the container.
When the pressure increases, the slider can be moved upwardly, against the force of an elastic means, thereby disactivating the connecting means and making the grip member free to rotate with respect of the closure member.
When the pressure decreases to an acceptable level which is no longer dangerous, the slider is lowered by the elastic means thereby activating the connecting means which allows the rotation of the closure member, through the rotation of the grip member, for removing the closure member from the aperture of the container.
In conventional safety caps, the seal between the slider and the closure member is usually provided by an O-ring.
It is apparent that, after a while, the O-ring will not guarantee a perfect seal between the surfaces of the slider and of the closure member allowing more or less vapor to escape.
While inconvenience may seem to be of no consequence, it actually completely impairs the correct operation of the safety cap.
In fact, the displacement of the slider by the elastic means, such as a spring, is modified by the pressure inside the container which is in turn modified by the leaks between the slider and the closure member.
In other words, the pressure inside the container may not reach a value high enough to allow the slider to move upwardly against the elastic means preventing a secure disengagement between the grip member and the closure member which may be removed from the container with fatal consequences.
Furthermore, when the vapor leaks between the slider and the closure member surfaces, it tends to condense and leave calcareous deposits on the same surfaces, on the O-ring and on the connecting means which eventually impair the correct operation of the cap.